Prestretched expanded metal and method of making it

ABSTRACT

After production of expanded metal in substantially the usual way, sheet is stretched longitudinally until the strands in at least some of the rows become substantially longitudinally aligned. Punch may be shifted a distance equal to about one-third the tooth width to produce asymmetric diamond-shaped openings prior to stretching. Sheet may be bent longitudinally upon itself along a row of aligned strands to yield a smooth edge. Electrode may be formed by applying a chemically active powder to sheet.

United States Patent Assignee Inventor John A. Brownrlgg Redding Ridge,Conn. 715,049

Mar. 21, 1968 Sept. 21, 1971 Exmet Corporation Appl. No. Filed PatentedPRESTRETCHED EXPANDED METAL AND METHOD OF MAKING IT 13 Claims, 22Drawing Figs.

11.8. CI 136/37, 29/6. 1 29/l93.5, 52/635 Int. Cl H01m35/04, B21c 37/00Field of Search 136/37, 36, 38, 20, 28, 30; 29/61, 6.2, 193.5; 72/392;52/635, 670, 672

References Cited UNITED STATES PATENTS 1,982,485 11/1934 Salmon et a1.136/36 2,261,053 10/1941 De Martis et al. 136/37 3,069,486 12/1962Solomon et a1. 136/30 3,180,761 4/1965 Horn et al 136/51 3,310,4383/1967 Huffman et a1. 136/38 Primary Examiner-Allen B. Curtis AssistantExaminer-C. F. Lefevour Attorney-Breitenfeld and Levine ABSTRACT: Afterproduction of expanded metal in substantially the usual way, sheet isstretched longitudinally until the strands in at least some of the rowsbecome substantially longitudinally aligned. Punch may be shifted adistance equal to about one-third the tooth width to produce asymmetricdiamond-shaped openings prior to stretching. Sheet may be bentlongitudinally upon itself along a row of aligned strands to yield asmooth edge. Electrode may be formed by applying a chemically activepowder to sheet.

PATENTEU SEP21 I97! 3,607,411

SHEET 3 BF 3 FIG; 20

BY W 4 ATTORNEYS PRESTRETCI-IED EXPANDED METAL AND METHOD OF MAKING ITThis invention relates to expanded metal, and more particu larly toexpanded metal having reduced longitudinal stretchability, the termlongitudinal" referring to the direction in which the metal sheet isadvanced during the expanding procedure.

Expanded metal is in itself well known. It is a sheet or web of metalhaving longitudinal rows of diamondor hexagonalshaped openings, theopenings in adjacent rows being separated by expanded strands, and theadjacent openings in each row being separated by connecting bridgesbetween the strands. Each strand extends between two connecting bridgesat an acute angle to the longitudinal direction of the web.

When the expanded metal web is intended for certain end uses, theexpanded strands are made of very fine gauge (e.g., 0.005-inch materialthickness, 0.0l-inch strand width) and the expanded metal web is runlongitudinally through additional equipment to further process it. Forexample, in the manufacture of electrodes for electrochemical cells,expanded metal is processed so as to apply a chemically active powder toit. During this further processing, the web is subjected to longitudinalpulling and as a result the strands have a tendency to rotate abouttheir ends in a direction which brings them closer to alignment with thedirection of the pulling force, i.e., the longitudinal direction. Thisreaction to longitudinal pulling causes certain problems. Rotation ofthe strands toward the longitudinal direction causes a correspondingnarrowing of the web. However, since the amount that different strandsrotate is not uniform, due in part to the fact that different parts ofthe web may be subjected to different pulling forces, the web becomesdistorted since it narrows in a nonuniform and unpredictable manner.Furthermore, the sizes of the openings in the web become nonuniform.

It is an object of the present invention to overcome these and otherproblems by providing expanded metal which has greatly reducedlongitudinal stretchability, regardless of how fine the gauge of itsstrands.

It is another object of the invention to provide expanded metal havingan increased proportion of the sheet area occupied by openings, ascompared to an otherwise identical sheet expanded by the same punchdriven to the same depth of penetration.

It is a further object of the invention to provide a method forproducing such expanded metal.

To achieve these objectives, the invention contemplates making expandedmetal substantially in the usual way on conventional metal-expandingequipment, and thereafter stretching it longitudinally, in a controlledmanner with uniformly applied force along its entire length, to bringall the strands in at least some of the rows into longitudinalalignment. This stretching is done prior to any further processing ofthe expanded metal web, so that no additional stretching takes placeduring such processing. An additional benefit of the stretchingoperation is that the connecting bridges between the strands in adjacentrows are rotated toward a position perpendicular to the plane of thesheet, thus increasing the overall thickness of the material.Consequently, the materialholding capability of the openings isincreased.

If the punch moves through a distance equal to one-half the width of onetooth during each lateral reciprocation, openings in the shape ofsymmetrical diamonds or hexagons are formed in the sheet. On the otherhand, if the punch moves a different distance during each lateralreciprocation, say one-third the tooth width, openings in the shape ofasymmetrical diamonds are formed. In the former case, the prestretchingprocedure serves to align all the strands longitudinally, but in thelatter case, because the strands in every other row are shorter, onlythey are aligned longitudinally.

A feature of the invention involves the fact that an expanded metalsheet stretched according to the present invention can readily beprovided with a smooth longitudinal edge by simply bending the sheetupon itself along a longitudinal row of aligned strands.

Additional features and advantages of the invention will be apparentfrom the following description in which reference is made to theaccompanying drawings.

In the drawings:

FIG. 1 is a fragmentary elevational view of a conventional shear plateand punch at the commencement of a sequence of operations resulting information of expanded metal;

FIGS. 2-5 are similar views of successive operations;

FIG. 6 is a cross-sectional view along line 66 of FIG. 4;

FIG. 7 is a view similar to FIG. 6 showing a subsequent step in theprocess;

FIG. 8 is a cross-sectional view along line 8-8 of FIG. 5;

FIG. 9 is a face view of a piece of the resultant conventional expandedmetal;

FIG. 10 is a view similar to FIG. 9 after stretching of the sheetaccording to this invention; 7

FIG. 11 is a schematic elevational view of apparatus for stretching theweb;

FIGS. 12-16 are views similar to FIGS. l-5, showing an alternativeembodiment of the invention;

FIG. 17 is a face view of a piece of the expanded metal resulting fromthe procedure of FIGS. 12-16;

FIG. 18 is a view similar to FIG. 17 after stretching of the sheet;

FIG. 19 is a face view of a piece of stretched expanded metal bent uponitself to produce a smooth edge;

FIG. 20 is a cross-sectional view along line 2020 of FIG. 19;

FIG. 21 is a fragmentary face view of an electrode incorporating a pieceof stretched expanded metal according to this invention; and

FIG. 22 is a cross-sectional view along line 22-22 of FIG. 21.

The size of expanded metal shown in the drawings has been greatlyexaggerated for the sake of clarity of illustration. In fact, thepresent invention relates to products wherein a typical cross-sectionaldimension of a strand is of the order of 0.008 inch.

Referring to FIGS. 1-8, a shear plate 20 and punch 21 are arranged inshearing relationship. A sheet of metal 22 to be treated is advancedintermittently (in the direction of the observer in FIGS. 1-5) to bringsuccessive regions into an overhanging relation to the shear plate 20and thus subject them to the shearing action of the punch 21. Theseadvancements of the metal 22 occur during periods that the punch 21 iswithdrawn from the shear plate (FIGS. 1, 3, and 5). During these periodsthere is also a relative lateral shift of the punch 21 and sheet 22. Thepunch 21 is serrated, i.e., it has teeth 23 separated by recesses ordepressions 24. These can be shaped or contoured in various ways toproduce correspondingly different effects. For example, in FIGS. l-5,each tooth 23 is blunted so that it terminates in a relatively longtooth flat 25.

Assuming in FIG. 1 that the sheet 22 is in a position in which itsadvancing margin overhangs the edge of the shear plate 20 by the desiredamount, the punch 21 is now caused to descend to its lowest positionshown in FIG. 2. This shears and expands the strands 28, whichnevertheless remain connected to the parent sheet in the regions 29between the teeth 23 of the punch 21. The punch then withdraws andshifts laterally relative to sheet 22, as indicated by the arrows inFIG. 3. In the case of FIGS. 1-5, the amount of lateral shift equalsone-half the width of one tooth 23, i.e., one-half the distance from thecenter of one depression 24 to the center of the next successivedepression.

During the period of lateral shift, the sheet 22 advances again to bringthe next successive region into shearing position. On the next descentof the punch 21 (FIG. 4), the teeth encounter the regions 29 therebyshearing and expanding the next row of strands 30. These are similarlyretained in connected relation to the parent sheet in the regions 31between the teeth 23 of the punch. Again, the punch 21 withdraws (FIG.5) and shifts back to the position of FIG. 1 while the sheet 22 advancesagain. This sequence of steps is repeated as often as desired. Theresultant product 33 is shown in FIG. 9, there being successivestaggered transverse rows of sheared and expanded strands linkedtogether by connecting bridges. In FIG. 9, the two rows at the bottomare numbered to correspond to the procedural steps described inconnection with FIGS. 1-8.

It will be seen in FIG. 9 that the openings 32 in the expanded metalsheet 33 have the shape of symmetrical hexagons, each opening beingdefined by four strands 28, 30, or 34 (hereinafter referred tocollectively by the numeral 34), and two connecting bridges 29, 31, or35 (hereinafter referred to collectively by the numeral 35). Therelatively long connecting bridges result from the use of relativelylong flats on the teeth 23 of the punch, and limiting the depth ofpenetration of the punch to that shown in FIGS. 2 and 4. The symmetry ofthe hexagons is a result of shifting the punch laterally a distanceequal to precisely one-half the width of a tooth 23. Each strand 34extends at an acute angle to the longitudinal direction of the sheet 33(the longitudinal direction being the direction in which the sheetadvances as it moves between the punch 21 and shear plate 20, i.e., thevertical direction in FIG. 9) between connecting bridges 35 in twoadjacent longitudinal and transverse rows. Due to the angled conditionof the strands 34, when the web 33 is subjected to a longitudinalstretching force, each strand has a tendency to rotate about the pointsat which it is connected to its respective connecting bridges toward aposition of alignment with the longitudinal direction of the web.

Therefore, according to this invention, fine gauge expanded metal whichis to be further processed in such a way that it is subjected tolongitudinal pulling forces is prestretched after its manufacture, asdescribed above, and before it is further processed. Prestretching maybe accomplished in a number of ways. For the purposes of the presentinvention, any stretching apparatus which applies a uniform longitudinalforce to the expanded metal web along its entire length may be employed.Such an apparatus is shown schematically in FIG. 11, and includes twopairs of nip rollers 38 and 39 between which the expanded metal web 33passes from left to right. The web is gripped by the rollers, and thefront rollers 38 rotate faster than the rear rollers 39, whereby the webexperiences stretching in the region between the rollers. To insureuniform stretching of the web, the pulling force on the web can bemonitored continuously and variations in this force from a predeterminedstandard used to vary the speed of one of the pairs of rollers tocompensate for the force variations. In the alternative, the frontrollers may be driven through a magnetic clutch (not shown) adjusted toslip when the pulling force exceeds a predetermined standard.

The predetermined standard pulling force applied to the web 33 should bea force which is just sufficient to bend the metal, in the regions atwhich the strands 34 join the connecting bridges 35, beyond its elasticlimit and to a degree sufficient to bring the strands 34 in eachlongitudinal row into substantially longitudinal alignment, as shown inFIG. 10. Several characteristics of the original expanded metal web ofFIG. 9 have been altered by stretching it to the condition of FIG. 10.The length of the web has been increased and its width decreased. Moreimportant, the web of FIG. 10 is practically unstretchable in alongitudinal direction, and the openings 32 occupy a larger proportionof the face area of the web of FIG. 10 than in the case of the FIG. 9web. Furthermore, the connecting bridges 35 are closer to beingperpendicular to the plane of the sheet. Thus, the effective thicknessof the sheet is increased. This effect, together with the increase inthe proportion of openings, serves to increase the material holdingcapacity of the sheet. The significance of this will be seen below withreference to the electrode of FIGS. 21 and 22.

An alternative embodiment of the invention is illustrated in FIGS.12-18. In general, the apparatus of FIGS. 12-16 is the same as that ofFIGS. 1-5, with the exception that the teeth 53 of punch 51 are morepointed, i.e., the long tooth flat 25 has been eliminated, or at leastgreatly minimized. However, the shear plate 50, and the sheet metal 52which is acted upon, may be identical to the corresponding parts 20 and22. One other distinction involves the fact that during the lateralshifting of the punch 51, the latter does not move through a distanceequal to one-half the tooth width as does the punch 21, but insteadthrough a distance other than a whole number multiple of one-half thetooth width. In the example illustrated, the shift distance equalsone-third the tooth width.

When the punch 51 descends from the position of FIG. 12 to that of FIG.13, strands 58 are sheared and expanded, but remain connected to theparent sheet in the regions 59 between the teeth 53. The punch thenwithdraws and shifts laterally, as indicated by the arrows in FIG. 14,during which period the sheet 52 advances. The next descent of the punch51 (FIG. 15) produces the next transverse row of sheared and expandedstrands 60L and 608, connected to the parent sheet in the regions 61.These strands are not all of equal length, as is true of the strands 28,30, and 34 of FIGS. 1-9. Instead, every other strand in the transverserow is relatively long, and is identified by the reference numeral 60L,and the alternate strands are relatively short, and identified by thereference numeral 608. The punch again withdraws and shifts laterally,as indicated in FIG. 16, and the process is repeated.

The resultant product 63 is shown in FIG. 17 the openings 62 having theshape of asymmetric diamonds. The asymmetry results from the fact thatthe punch is shifted laterally a distance which is a fraction ofone-half the width of a tooth 53. Each opening 62 is defined by twoadjacent short strands, e.g., 60S and 64S, and two adjacent longstrands, e.g., 60L and 64L (hereinafter all short strands will bereferred to by the numeral 645, and all long strands by the numeral64L). Each long strand 64L is bent near one end, and the bent portionoverlaps a portion of its adjacent long strand. However, the overlappedportions of the long strands are unconnected except at the connectingbridges 59, 61, and 65.

Since the strands are all arranged at an acute angle to the longitudinaldirection of the expanded metal web 63 of FIG. 17, these strands alsohave a tendency to rotate about their points of connection to theirrespective connecting bridges when a longitudinal pulling force isapplied to the web. Therefore, it is desirable to subject the web ofFIG. 17 to the action OF the apparatus of FIG. 11 so as to produce theproduct shown in FIG. 18. With the web in the stretched condition ofFIG. 18, the short strands 648 of each longitudinal row are insubstantially longitudinal alignment, the short strands occupying everyother longitudinal row. However, the long strands 64L, occupying thealternate rows, are arranged in a sawtooth pattern. Due to thesubstantial alignment of the strands 648, the web 63 of FIG. 18 ispractically unstretchable in a longitudinal direction. In addition, theproportion of the total area of the sheet occupied by the openings 62 inFIG. 18 is greater than the proportion occupied by the openings in F IG.17.

It should be pointed out that the term stretching" as used above and inthe following claims is intended to mean lengthening of the sheet or webof expanded metal as a whole by virtue of rotation of the strands, anddoes not contemplate lengthening of the individual strands.

A benefit of prestretched expanded metal as described above, andillustrated in FIGS. 10 and 18 resides in its ability to be readilyprovided with a smooth longitudinal edge. One of the problems presentedby conventional expanded metal is that its longitudinal edges areragged. It has been found that if prestretched expanded metal accordingto this invention is bent upon itself, as shown in FIGS. 19 and 20,along a longitudinal line, it inherently tends to bend along alongitudinally aligned row of strands 648. Since the strands of thisrow, now located along the longitudinal edge of the sheet, are allinterconnected and present no sharp cut edges, the bent longitudinaledge of the sheet is smooth.

As mentioned above, one use of prestretched expanded metal as describedabove is in the formation of electrodes for electrochemical cells, suchas of nickel-cadmium, silver-zinc,

or metal-air batteries. A portion of such an electrode is shown in FIGS.21 and 22. It will be noted that the electrode has been formed byfilling the openings 32 of the sheet with a suitable chemically activepowder 70. The more common powdered materials used for this purpose arezinc, silver, nickel, zinc oxide, and silver oxide. The powder may beapplied to the expanded metal in a number of ways. For example, theprestretched expanded metal sheet may be pulled through a slurrycontaining the powder, the excess slurry doctored off both faces of thesheet, and the sheet dried. The finished electrode may be used in aconventional manner in an electrochemical cell.

The invention has been shown and described in preferred form only, andby way of example, and many variations may be made in the inventionwhich will still be comprised within its spirit. It is understood,therefore, that the invention is not limited to any specific form orembodiment except insofar as such limitations are included in theappended claims.

What is claimed is:

1. A sheet of expanded metal having a longitudinal direction defining alongitudinal axis and rows of openings in said longitudinal direction,said openings being delimited by strands defining the lateral boundariesof the openings and connecting bridges between the strands defining theforward and rearward boundaries of the openings said connecting bridgesbeing substantially perpendicular to, the longitudinal axes of all thestrands along at least one side of each row of openings beingsubstantially aligned and substantially parallel to all the otheraligned rows of strands, the longitudinal axes of said aligned strandsextending along the longitudinal direction of the sheet.

2. A sheet of expanded metal as defined in claim 1 wherein thelongitudinal axes of all the strands along each side of each row ofopenings are substantially aligned and substantially parallel to all theother aligned rows of strands.

3. A sheet of expanded metal as defined in claiin 2 wherein all saidsubstantially aligned strands are substantially perpendicular to theconnecting bridges to which they are connected.

4. A sheet of expanded metal as defined in claim 1 wherein thelongitudinal axes of the strands in only every other row aresubstantially aligned, the strands in the alternate rows being arrangedin a sawtooth pattern.

5. A sheet of expanded metal as defined in claim 4 wherein saidconnecting bridges are arranged in longitudinally spacedapart transverserows, each strand of the sawtooth pattern extending between a connectingbridge located at the intersection of one of said transverse rows andone of said aligned rows of strands and another connecting bridgelocated at the intersection of the next successive transverse row andthe next successive aligned row of strands.

6. A sheet of expanded metal as defined in claim 5 wherein each twosuccessive strands of the sawtooth pattern are arranged at an obtuseangle to each other.

7. A sheet of expanded metal as defined in claim 1, said sheet beingbent upon itself along a longitudinal row of aligned strands, said rowof aligned strands thereby forming a smooth longitudinal edge of thesheet.

8. A method of making a sheet of expanded metal comprising the steps ofadvancing sheet metal along its longitudinal axis in stepwise fashionrelative to a toothed punch, operating the punch between each twosuccessive advancing steps to partially sever the sheet therebyproviding parallel rows of openings, said rows of openings beingparallel to said longitudinal axis and each opening defined by a seriesof strands separated by connecting bridges said bridges beingsubstantially perpendicular to the longitudinal axis, and thereafterstretching the expanded metal sheet in said longitudinal directionbeyond its elastic limit until the longitudinal axes of the strands inat least some of the rows become substantially longitudinally aligned.

9. A method as defined in claim '8 wherein the punch is shiftedlaterally a distance other than a whole number multiple of one-half thewidth of one punch tooth between each two successive operations of thepunch.

10. A method as defined in claim 8 wherein the punch 18 shiftedlaterally a distance about equal to one-third the width of one punchtooth between each two successive operations of the punch.

11. An electrode for an electrochemical cell, comprising a sheet ofexpanded metal having openings delimited by strands defining the lateralboundaries of the openings and connecting bridges between the strandsdefining the forward and rearward boundaries of the openings, thelongitudinal axes of all the strands along at least one side of each rowof openings being substantially aligned and substantially parallel toall the other aligned rows of strands, the longitudinal axes of saidaligned strands extending along the longitudinal direction of the sheet,and a chemically active powder within said openings.

12. An electrode as defined in claim 11 wherein said powder is selectedfrom the class consisting of zinc, silver, nickel, zinc oxide, andsilver oxide.

13. A method of making a sheet ofexpanded metal comprising the steps ofadvancing sheet metal along its longitudinal axis in stepwise fashionrelative to a toothed punch, operating the punch between each twosuccessive advancing steps to partially sever the sheet therebyproviding parallel rows of openings, said rows of openings beingparallel to said longitudinal axis and each opening defined by a seriesof strands con nected at their ends to connecting bridges said bridgesbeing substantially perpendicular to the longitudinal axis, the strandsbeing arranged at an angle to the longitudinal direction of advance ofthe sheet, thereafter stretching the expanded metal sheet in saidlongitudinal direction to cause rotation of the strands about theirends, and continuing said stretching until said rotation ceases and thelongitudinal axes of the strands in at least some of the rows becomesubstantially longitudinally aligned.

2. A sheet of expanded metal as defined in claim 1 wherein thelongitudinal axes of all the strands along each side of each row ofopenings are substAntially aligned and substantially parallel to all theother aligned rows of strands.
 3. A sheet of expanded metal as definedin claim 2 wherein all said substantially aligned strands aresubstantially perpendicular to the connecting bridges to which they areconnected.
 4. A sheet of expanded metal as defined in claim 1 whereinthe longitudinal axes of the strands in only every other row aresubstantially aligned, the strands in the alternate rows being arrangedin a sawtooth pattern.
 5. A sheet of expanded metal as defined in claim4 wherein said connecting bridges are arranged in longitudinallyspaced-apart transverse rows, each strand of the sawtooth patternextending between a connecting bridge located at the intersection of oneof said transverse rows and one of said aligned rows of strands andanother connecting bridge located at the intersection of the nextsuccessive transverse row and the next successive aligned row ofstrands.
 6. A sheet of expanded metal as defined in claim 5 wherein eachtwo successive strands of the sawtooth pattern are arranged at an obtuseangle to each other.
 7. A sheet of expanded metal as defined in claim 1,said sheet being bent upon itself along a longitudinal row of alignedstrands, said row of aligned strands thereby forming a smoothlongitudinal edge of the sheet.
 8. A method of making a sheet ofexpanded metal comprising the steps of advancing sheet metal along itslongitudinal axis in stepwise fashion relative to a toothed punch,operating the punch between each two successive advancing steps topartially sever the sheet thereby providing parallel rows of openings,said rows of openings being parallel to said longitudinal axis and eachopening defined by a series of strands separated by connecting bridgessaid bridges being substantially perpendicular to the longitudinal axis,and thereafter stretching the expanded metal sheet in said longitudinaldirection beyond its elastic limit until the longitudinal axes of thestrands in at least some of the rows become substantially longitudinallyaligned.
 9. A method as defined in claim 8 wherein the punch is shiftedlaterally a distance other than a whole number multiple of one-half thewidth of one punch tooth between each two successive operations of thepunch.
 10. A method as defined in claim 8 wherein the punch is shiftedlaterally a distance about equal to one-third the width of one punchtooth between each two successive operations of the punch.
 11. Anelectrode for an electrochemical cell, comprising a sheet of expandedmetal having openings delimited by strands defining the lateralboundaries of the openings and connecting bridges between the strandsdefining the forward and rearward boundaries of the openings, thelongitudinal axes of all the strands along at least one side of each rowof openings being substantially aligned and substantially parallel toall the other aligned rows of strands, the longitudinal axes of saidaligned strands extending along the longitudinal direction of the sheet,and a chemically active powder within said openings.
 12. An electrode asdefined in claim 11 wherein said powder is selected from the classconsisting of zinc, silver, nickel, zinc oxide, and silver oxide.
 13. Amethod of making a sheet of expanded metal comprising the steps ofadvancing sheet metal along its longitudinal axis in stepwise fashionrelative to a toothed punch, operating the punch between each twosuccessive advancing steps to partially sever the sheet therebyproviding parallel rows of openings, said rows of openings beingparallel to said longitudinal axis and each opening defined by a seriesof strands connected at their ends to connecting bridges said bridgesbeing substantially perpendicular to the longitudinal axis, the strandsbeing arranged at an angle to the longitudinal direction of advance ofthe sheet, thereafter stretching the expanded metal sheet in saidlongitudinal direction to cause rotation of the strands about theiRends, and continuing said stretching until said rotation ceases and thelongitudinal axes of the strands in at least some of the rows becomesubstantially longitudinally aligned.